This invention relates to the hydraulic actuation of intake and exhaust valves in an internal combustion engine. Many camless, i.e. direct valve actuation techniques have been developed, most of which work on a common rail basis, if they are hydraulic or pneumatic, or electro-magnetically if they are not. Other means have been developed to change the phase relationship of conventional camshafts with the crankshaft over the speed range. Solenoid venting valves have been used in conjunction with hydraulic tappets to keep valves closed, thereby disabling cylinders for improved part load efficiency. The approach described here is fundamentally different. Its objectives are the same as the other camless techniques but it aims to achieve them with much reduced parasitic power loss and complexity.
The fluid-working machine described in EP-B-361927 uses cycle-by-cycle mode selection of its positive displacement pumping chambers. We have discovered that an extension of this technique to control the phasing and duration of a cyclic linear fluid actuation, working at the frequency of the input shaft, can be used to open and shut intake and exhaust valves in internal combustion engines.